'Sherlock' Season 4 Spoilers and Air Date: Will the Moriarty Mystery be Solved in the Christmas Special?

Season 4 of "Sherlock" will air only in early 2017, as filming is set to commence sometime in spring 2016.

"Sherlock" fans will have to wait until 2017 to get a glimpse of season 4 of the detective drama, as it was recently revealed that filming for the next season wouldn't start until spring 2016.

This announcement by showrunner Steven Moffat has helped debunk rumours that fans will get to see the next three episodes of the show by early 2016. But before the next season airs, fans will get to see Benedict Cumberbatch's Sherlock Holmes and Martin Freeman's John Watson trying to solve a mystery in a one off Christmas special that will air towards the end of the year.

The Christmas special will be Victorian-themed, and according to an earlier interview Moffat had with Entertainment Weekly, the special episode is not part of the three-episode run.

"The special is its own thing," said Moffat. "We wouldn't have done the story we're doing, and the way we're doing it, if we didn't have this special. It's not part of the run of three episodes. So we had this to do it – as we could hardly conceal – it's Victorian. [Co-creator Mark Gatiss] and me, we wanted to do this, but it had to be a special, it had to be separate entity on its own. It's kind of in its own little bubble."

It remains to be seen how the Moriarty mystery will be addressed in this special. But Gatiss revealed to Radio Times last year that the one-off special will completely solve the mystery. Moriarty was presumed dead in season 2 finale when he shot himself through the head after convincing Sherlock to do the same. However, season 3 ended with the return of the villain who took over television networks across London with the question "Did you miss me?"

Is Moriarty really alive? Actor Cumberbatch is one of the few persons who knows the answer to the Moriarty mystery, but he has refrained from talking about it, and at one point even said he was trying to forget the details of Moriarty's return.

"I like casually forgetting, not least because there's a lot of other traffic between then and now but also because it's more fun because it's slightly more fresh. It's a very good idea, I do remember that detail. I'm just trying not to remember it so I don't blurt it out," Cumberbatch said last year, according to MTV.